For almost 40 years a debated raged until Robert Dicke proposed that the big bang would have produced a flash of light still present everywhere as a glow of radio waves. In 1965 Arno Penzias and Robert Wilson unmistakably found that glow, now called the Cosmic Microwave Background Radiation (CMBR).
The debate was over. Our universe, the totality of all things, had a fiery beginning about 15 billion years ago. Click here to read more about "The Big Bang".
Note: This video was broadcast on PBS on October 20, 1997.
Superposed on an optical picture of a group of galaxies is an X-ray image taken by ROSAT. The image shows confined hot gas (which produces X-rays) highlighted in false red color. The presence of this confined gas indicates that the gravity exerted in groups and clusters of galaxies is larger than that expected from the observed galaxies.